The present invention relates to a circuit for referring to vector data in a main storage of a digital computer suitable for executing a fast vector processing (to be referred to as a vector processor herebelow) based on a virtual address. A vector processor has been developed for high-speed processing, for example, a large-sized matrix calculation frequently appearing in a scientific and engineering calculation. An example of such a vector processor has been described in the U.S. Pat. No. 4,128,880.
On the other hand, there has been used a virtual address system which allows an address space to exceed the main storage capacity of a computer. A scheme for achieving such a virtual address system has been discussed in the Structured Computer Organization (Prentice-Hall Inc., 6.4 Virtual Memory, pp. 308-341) written by A. S. Tanebaum.
There has also been a vector processor in which the virtual address system is implemented. However, the prior art vector processor configured in the virtual address system has the following problem.
In the virtual address system, when an address translator detects that a data item which is required to be found in the main storage is missing therein, a page fault interruption takes place and the operating system (OS) effects processing (paging) for transferring data from an auxiliary storage to the main storage. Thereafter, the contents of an address translation table are changed to allow the data transferred and stored in the main storage to be accessed after this point, and then the original processing interrupted is resumed. Such a processing in which the data is reserved by use of paging when the data becomes necessary is called on-demand paging in general.
The conventional vector processor has also adopted the on-demand paging. That is, as shown in FIG. 1, a paging processing 12 is first initiated only when the vector data is necessary. The vector processing 10 is interrupted for a period of time required by the paging processing, which leads to a problem that the vector processing time is undesirably increased.